2933.59.21.00 - Antihistamines, including those principally used as anti-nauseants

This HTS classification, 2933.59.21.00, specifically enumerates antihistamines. This category encompasses chemical compounds primarily functioning to block the action of histamine in the body, thereby alleviating allergic reactions. Crucially, it also includes those antihistamines that are principally formulated and used for their anti-nauseant properties, often prescribed to manage motion sickness or post-operative nausea and vomiting. The defining characteristic is their pharmacological action as antihistamines, regardless of secondary anti-nauseant applications.

Distinguishing this category from its siblings, it is important to note that while 2933.59.46.00 covers antidepressants, tranquilizers, and other psychotherapeutic agents, and 2933.59.53.00 is a residual "Other" category for drugs within this heterocyclic ring structure, 2933.59.21.00 is narrowly focused on compounds acting as antihistamines. The "Anti-infective agents" sibling category would encompass compounds used to treat infections, which is distinct from the immunological and receptor-blocking mechanisms of antihistamines.

As this is a leaf node, there are no further subdivisions. Classification within 2933.59.21.00 is determined by the compound's primary intended use as an antihistamine, with a recognized secondary classification for those primarily serving as anti-nauseants, all within the broader context of heterocyclic compounds containing a pyrimidine or piperazine ring. The principal application and pharmacological profile are the key determinants for correct classification.